The present invention relates to a fuel injection apparatus of an internal combustion engine and, more particularly, to a fuel injection apparatus of a diesel engine which controls to effectively supply heterogeneous liquid fuel, such as an auxiliary fuel, which has good ignitibility with respect to a main fuel having poor ignitibility.
In the case of injecting two types of fuel in a diesel engine, alcohol is used as the main fuel and light oil is used as the auxiliary fuel. It has been proposed to add light oil having good ignitibility to alcohol having poor ignitibility, and to inject a mixture thereof into a cylinder. However, it is known that in consideration of its ignitibility such a mixture has a limited mixing ratio. Therefore, when two different types of fuel are used, the main fuel and auxiliary fuel must not be mixed with each other. For example, light oil and alcohol must be separately injected into the cylinder. Alternatively, light oil having good ignitibility is first injected into the cylinder, and alcohol having poor ignitibility is then injected thereinto so as to form a two-layer structure.
Conventionally, means for injecting two different types of fuel are used as indicated by the following items (A) to (C):
(A) two injection pumps are used for the main fuel and the auxiliary fuel, respectively; PA0 (B) the negative pressure of a delivery valve is utilized; and PA0 (C) the pulsating effect of the injection system is utilized.
The fuel injecting means in item (A) comprises two sets of injection pumps and corresponding nozzles for the two types of fuel, respectively. Various reports have been made concerning use of the above-mentioned means in a variety of applications. The fuel injection means of this type requires two fuel injection control systems for each cylinder.
An example of the fuel injection means described in item (B) is disclosed in Japanese Patent Publication No. 51-13806. An auxiliary fuel source is connected at an arbitrary position of a path extending from the delivery valve of a main fuel injection system to an injection nozzle through a check valve. The auxiliary fuel is supplied by the negative pressure of the delivery valve to the fuel injection system through the check valve, thereby injecting the main fuel together with the auxiliary fuel from the injection nozzle.
However, in principle, in a fuel injection means utilizing the negative pressure of the delivery valve, a retraction or unloading amount must be increased. Therefore, the cavitation factor is increased degrading durability. The cavitation formed in the injection system due to retraction (i.e., the inlet amount of auxiliary fuel) varies irregularly in accordance with the driving speed and the load. As a result, it is impossible to properly control the inlet quantity of auxiliary fuel.
An example of the fuel injection means described in item (C) is disclosed in Japanese Patent Publication No. 50-23455. According to this fuel injection means, two injection nozzles are disposed for each cylinder. One of the injection nozzles is connected to a fuel pump, and the other thereof is connected to a water tank and a piston operated by the force of fuel compressed and supplied by the fuel pump. Water is sprayed to decrease the combustion temperature of the combustion chamber. The fuel injection means of this type becomes complicated, resulting in inconvenience.